1. Field of the Invention
The present invention relates to high altitude, solar powered aircraft, and more particularly to a wing design for long-term, high altitude flight of a solar powered aircraft.
2. Description of the Related Art
A solar-powered aircraft is one which derives energy from the sun by means of photovoltaic solar cells. This energy may be transformed for use in an electric motor to power the aircraft. Excess energy is stored either as potential energy in the form of increased altitude of the aircraft, or as energy stored onboard in batteries or in some other energy storage system. The stored energy is used to keep the vehicle aloft during the night so that flight time is not limited by fuel supply as it is on a conventional aircraft.
A vehicle such as this must be able to fly at an altitude high enough to be above the clouds so as to collect the maximum amount of solar radiation possible, and to avoid winds with velocities much higher than the airspeed of the vehicle. Because of its long endurance and limited weight carrying ability, this type of vehicle is normally considered to be a pilotless aircraft.
The prior art discloses solar-powered aircraft of conventional configuration with solar cells on top of the wing or fuselage. U.S. Pat. No. 3,089,670 describes an aircraft where the wing surfaces are provided with solar cells, while U.S. Pat. No. 3,744,865 discloses a rotary type aircraft with solar cells located on rotor blades. Both of these aircraft enjoy maximum energy availability when the sun is directly overhead, but the energy decreases as a function of the cosine of the angle from the normal to the plane of the solar cells. Operation of such solar powered aircraft is therefore limited by the position of the sun.
One desired capability of a solar powered aircraft is its ability to remain airborne for an indefinite period of time. Another is that it should have unlimited range and not be limited to a single location. Still another is that the craft should be able to position itself so that the solar energy capturing cells are always positioned normal to the rays of the sun.
To accomplish these ends, the craft must be able to recover the maximum possible solar energy throughout the daytime hours. For the craft to have unlimited range, it must be able to convert such stored solar energy to usable form during the nighttime hours. For the solar energy capturing cells to be disposed normal to the sun's rays, the aircraft must be able to tilt or bank as the sun moves relative to the earth's axis.